Retire public ingress monitor CLI

[cbusillo]

Summary

• remove the local public-ingress-monitor run-once CLI mutation surface
• keep the FastAPI service route and GitHub workflow as the supported rerun path
• update compatibility and operations docs, plus a retirement assertion test

Validation

• uv run python -m unittest tests.test_public_ingress_monitor.PublicIngressMonitorCliTests
• uv run python -m unittest tests.test_public_ingress_monitor tests.test_http_app.FastApiPublicIngressMonitorTests
• uv run python -m unittest
• uv run --extra dev ruff check control_plane/cli.py tests/test_public_ingress_monitor.py
• uv run --extra dev ruff format --check control_plane/cli.py tests/test_public_ingress_monitor.py
• uv run --extra dev ruff check .
• uv run --extra dev mypy control_plane tests
• uv run launchplane service audit-config-authority --control-plane-root .
• JetBrains changed-files inspection: clean
• Review agents: no blocking findings

Note: uv run --extra dev ruff format --check . still reports unrelated pre-existing formatting drift outside this slice.

Refs #1322